Nuclear Reactor Shutdown Rods with Passive Float Control
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Solution Overview
Problem
Current nuclear reactors face challenges in rapid shutdown during accidents, as control rod insertion mechanisms are prone to failure and can be disrupted by uncontrolled pump acceleration, leading to excessive fuel heating.
Innovation Solution
A nuclear reactor design featuring shutdown rods with a float-controlled mechanism and non-return device, supported externally to the core, allowing for reliable and passive shutdown without interfering with thermal expansions and enabling refuelling without disconnecting control mechanisms, while reducing fissile material and core heterogeneity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If control rods are used for rapid shutdown, then shutdown speed is improved, but reliability deteriorates due to command processing failures and pump acceleration disruptions
Solution Approach 1:
The shutdown rod system uses passive float-controlled mechanisms that automatically activate during accidents without requiring external command signals. The float rises with coolant level during pump stoppage or uncontrolled acceleration, directly triggering rod insertion through mechanical linkage, eliminating dependency on vulnerable electronic control systems
Solution Approach 2:
The patent replaces electronic command-processing systems with a purely mechanical float-actuated mechanism. The float's buoyancy-driven motion directly translates to rod insertion through mechanical linkages and cam mechanisms, substituting unreliable electronic controls with fail-safe passive mechanical action
2Reliability
If shutdown rods are positioned within the core, then shutdown effectiveness is improved, but thermal expansion interference and refuelling complexity increase
Solution Approach 1:
The shutdown rod support structure is extracted from the core interior and repositioned in the upper plenum region above the core. This external positioning removes interference with fuel element thermal expansion and simplifies refuelling operations, while maintaining shutdown effectiveness through strategic rod insertion points
Solution Approach 2:
The shutdown rod support mechanism is relocated from the horizontal plane within the core to the vertical dimension in the upper plenum. This spatial reconfiguration allows rods to descend vertically into the core from above, avoiding interference with core internals and refuelling operations while preserving shutdown capability
3Ease of operation
If command-processing logics are used for control rod insertion, then operational control is improved, but failure risks increase due to system complexity
Solution Approach 1:
The system uses passive float-controlled mechanisms that automatically activate during accidents without requiring external command signals. The float rises with coolant level during pump stoppage or uncontrolled acceleration, directly triggering rod insertion through mechanical linkage, eliminating dependency on vulnerable electronic control systems
Solution Approach 2:
The design incorporates inherent fail-safety through passive mechanical mechanisms that are pre-configured to activate automatically under accident conditions. The float mechanism is pre-positioned to rise with coolant level, ensuring shutdown action occurs before damage can propagate, cushioning against the effects of control system failures
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution provides a reliable and diversified shutdown system that prevents excessive fuel heating during accidents, ensuring safe operation and reducing the risk of control mechanism deactivation, while allowing for efficient refuelling and minimizing fissile material and power gradients within the core.
Implementation Method 1
each rod (18) being provided with a float (26) consisting of a cylindrical casing (27) containing gas inside it which, as the level (H1) of the hot manifold (7) varies, determines the position of the neutron absorber (23) with respect to the active part (12) of the core (5) in a condition of disconnection from the control mechanism (28)
Data Source
Figure 1
Figure 2
Figure 3a~3c
AI summary
A nuclear reactor (1) comprises a vessel (2) closed at the top by a fixed closing structure (3) and a mobile closing structure (4) and containing a core (5) and a hydraulic separation structure (6) delimiting a hot manifold (7) and a cold manifold (8) in which a primary fluid (F) for cooling the core (5) circulates, with a first free surface (H1) in the hot manifold (7) which, during normal operation of the reactor (1), is different from a second free surface (H2) in the cold manifold (8); the core (5) comprises shutdown rods (18) which are operated by at least one float (26) which, via a down-up movement, positions respective neutron absorbers (23) in the vicinity of the active part (12) of the core when the level (H1) of the primary fluid (F) increases due to slowing down of the circulation pumps (9).